CO oxidation over titania-supported gold catalysts obtained using polyoxometalate
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CO oxidation over titania‑supported gold catalysts obtained using polyoxometalate G. M. Maksimov, et al. [full author details at the end of the article] Received: 28 August 2020 / Accepted: 24 September 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract The present work is devoted to the development of a versatile method of Au/TiO2 catalysts preparation using a polyoxometalate-based approach. It has been shown that the addition of polyoxometalates into an aqueous solution of A u3+ hydroxocomplexes has an evident stabilizing effect. Due to specified preparation conditions, the choice of the polyoxometalates is quite limited. The most convenient for this purpose compounds are niobium- and tungsten-containing polyoxometalates. Depending on preparation conditions and textural properties of used T iO2, dispersion of deposited gold particles can be varied within a range of 1–50 nm. The catalytic activity of the prepared Au/TiO2 catalysts is studied in a model reaction of CO oxidation. Besides the dispersion of Au particles, another key factor affecting the low-temperature activity of the Au/TiO2 catalysts in the CO oxidation is a reduction stage in the preparation procedures. Replace of hydrogen with CO results in the formation of more active and stable nanoparticles. Graphic abstract
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Vol.:(0123456789)
Reaction Kinetics, Mechanisms and Catalysis
Keywords Polyoxometalates · Titania support · Gold catalysts · TEM characterization · Thermal stability
Introduction During the last decades, synthesis of the supported gold materials has attracted great attention of the chemists mainly due to their wide applicability in catalysis [1–13]. For instance, in the field of catalysis by nanoparticles, gold catalysts stand the third position in the list of most studied systems [14]. As known, there are several approaches to obtain such materials [15–17]. The boom of the interest in the gold-containing systems has appeared when the Japanese researchers [18] have developed a relatively simple method of their preparation, which was named later as the deposition–precipitation approach. The idea of this method is based on the stirring of the powder support in an aqueous solution of H AuCl4 along with a simultaneous dosage of alkali into the suspension. All this results in the deposition of the Au3+ species on the support presumably in the form of hydroxyl complex, which can be easily reduced to A u0 state [18, 19]. The main advantage which should be mentioned is that the gold nanoparticles (NPs) being formed are very small in size (predominantly less than 4 nm) that is hardly accessible by using other methods. The catalysts containing such small nanoparticles were found to be extremely effective in various catalytic processes including low-temperature CO oxidation. On the other hand, the method is disadvantageously characterized by a quite limited possibility to adjust the particle size. Among other preparation methods of the Au/support materials, the method of Au0 particles sorption from the corresponding colloid
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